Counter-doped silicon carbide Schottky barrier diode

ABSTRACT

A Schottky diode includes an upper region having a first doping concentration of a first conductivity type, the upper region disposed above the SiC substrate and extending up to a top planar surface. First and second layers of a second conductivity type are disposed in the upper region adjoining the top planar surface and extending downward to a depth. Each of the first and second layers has a second doping concentration, the depth, first doping concentration, and second doping concentration being selected such that the first and second layers are depleted of carriers at a zero bias condition of the Schottky diode. A top metal layer disposed along the top planar surface in direct contact with the upper region and the first and second layers is the anode, and bottom metal layer disposed beneath the SiC substrate is the cathode, of the Schottky diode.

This application is a division of application Ser. No. 16/794,774, filedFeb. 19, 2020, entitled, “COUNTER-DOPED SILICON CARBIDE SCHOTTKY BARRIERDIODE”, which is assigned to the assignee of the present application.

TECHNICAL FIELD

The present disclosure relates to silicon carbide power semiconductordevices. More specifically, the present invention relates to siliconcarbide Schottky Barrier Diode (SBD) and Junction Barrier Schottky (JBS)diode structures capable of withstanding high voltages.

BACKGROUND

The Schottky diode (named after German physicist Walter H. Schottky) isa well-known semiconductor diode device that is achieved using ametal-semiconductor junction, frequently referred to as a Schottkybarrier, in contrast to an ordinary PN junction of a conventionalsemiconductor diode. Compared with silicon-based PIN diodes, siliconcarbide (SiC) Schottky barrier diodes (SBDs) are characterized by lowerswitching losses and very fast switching speed. However, SiC devices,due to their wider bandgap, are optimized to operate at higher electricfields. The leakage current across the reverse-biasedmetal-semiconductor junction in the SiC SBD at this higher electricfield is much higher than leakage across a PN junction of the samebarrier in a Si PIN diode.

Switching loss is low because, unlike silicon PIN diodes, SiC SBDs aremajority carrier devices that do not inject minority carriers into theN-type drift region. Since these carriers do not need to be removed toswitch the device off, the reverse current transient during switching issmall and the switching energy is negligible. This reduction inswitching energy has led to SiC SBDs replacing silicon PIN diodes inmany power applications such as the front-end boost converter inswitched-mode power supplies. One drawback with using SiC SBDs insteadof Si PIN diodes is enhanced reverse-biased leakage current.

Silicon SBDs are generally unsuitable for high voltage operation becausetheir reverse leakage current is relatively high, leading to highoff-state power dissipation. Even though the leakage current is muchsmaller in SiC SBDs as compared to silicon SBDs, reverse leakage in SiCSBDs is still a performance limitation. The leakage is due to electronsthat enter the semiconductor material from the metal by thermionic-fieldemission (TFE) under reverse bias. This leakage current increasesexponentially with the electric field at the metal-semiconductorinterface, i.e., where the semiconductor material directly contacts themetal forming the anode of the diode. The electric field is given by theslope of the conduction band at the surface.

Prior attempts to reduce the reverse leakage current in SiC SBDs havefocused on reducing the electric field at the surface. One past approachhas been to place isolated P⁺N junctions within the active area of theSBD. Such devices are commonly referred to as Junction-Barrier Schottky(JBS) diode structures. In JBS diodes, many of the electric field linesreaching the surface terminate on P⁺ N junctions rather than on theSchottky junction, thus reducing the surface electric field and hencelowering the reverse leakage current. One drawback of this approach,however, is that the insertion of P⁺N junctions increases the overallarea of the diode for the same current-carrying area of the Schottkyjunction, and thus increases the specific on-resistance in forward bias,and capacitance in reverse bias.

FIG. 1 is a cross-sectional view of a conventional prior art JBS diode10 that includes a top metal layer 11 in direct contact with a N-typedrift region 14 at a top surface 13 of the semiconductor material. Topmetal layer 11 forms the anode of JBS diode 10. Deep P+ regions 12 a &12 b are shown disposed at opposite lateral sides of top surface 13. AnN+ layer 15 vertically separates N-type drift region 14 from a bottommetal layer 16, which forms the cathode of JBS diode 10.

In JBS diode 10 deep P+ regions 12 a & 12 b are highly doped to aconcentration of 1E19/cm3 to 1E21/cm3, which is about 1000 times higheror more than the doping concentration of N-type drift region 14. P+regions 12 a & 12 b are typically formed to a vertical depth of 200 nmto 500 nm or more, with each P+ region having a lateral width of about2.0 μm. In conventional JBS diode 10 P+ regions 12 a & 12 b aretypically laterally separated by a distance of about 2.0 μm.

As discussed above, even though the JBS leakage current is less thanthat of a SiC SBD, the magnitude of the reverse bias leakage currentstill causes problems in certain applications. Furthermore, the additionof the highly-doped P+ regions reduces the Schottky diode contact area.The reduced contact area results in forward bias current reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified.

FIG. 1 is a cross-sectional diagram of a conventional JBS diode.

FIG. 2 is an example cross-sectional diagram of a SiC diode with acounter-doped Schottky barrier.

FIG. 3 is an example cross-sectional diagram of a JBS diode withcounter-doping in the Schottky region.

FIG. 4 is an example cross-sectional diagram of a trench JBS diode wherethe sidewalls of the trench and top surface of the SiC mesa arecounter-doped.

FIG. 5 is an example cross-sectional diagram of another trench JBS diodewhere the sidewalls of the trench are counter-doped and the top surfaceof the SiC mesa is not counter-doped.

FIG. 6 is chart showing reverse-bias leakage current performance resultsfor two embodiments of the JBS diode illustrated in FIG. 3 versus theconventional JBS diode of FIG. 1 .

Corresponding reference characters indicate corresponding componentsthroughout the several views of the drawings. Skilled artisans willappreciate that elements in the figures are illustrated for simplicityand clarity and have not necessarily been drawn to scale. For example,the dimensions of some of the elements in the figures may be exaggeratedrelative to other elements to help to improve understanding of variousembodiments of the disclosed subject matter. Also, common butwell-understood elements that are useful or necessary in a commerciallyfeasible embodiment are often not depicted in order to facilitate a lessobstructed view of these various embodiments presented. Additionally,persons of skill in the semiconductor arts will understand that regionsand elements depicted in cross-sectional diagrams should not be limitedto the particular shapes of the regions illustrated. For instance,implanted regions shown in rectangular form typically have rounded orcurved features due to normal fabrication processing. Thus, the shapesof regions shown in the drawings are not intended to illustrate theprecise shapes found in a manufactured device.

DETAILED DESCRIPTION

In the following description numerous specific details are set forth inorder to provide a thorough understanding of the disclosed subjectmatter. It will be apparent, however, to one having ordinary skill inthe art that the specific details need not be employed to practice thevarious embodiments described. In other instances, well-known systems,devices, or methods have not been described in detail in order to avoidobscuring the disclosed subject matter.

Reference throughout this specification to “one embodiment”, “anembodiment”, “one example” or “an example” means that a particularfeature, structure or characteristic described in connection with theembodiment or example is included in at least one embodiment of thedisclosed subject matter. Thus, appearances of the phrases “in oneembodiment”, “in an embodiment”, “one example” or “an example” invarious places throughout this specification are not necessarily allreferring to the same embodiment or example. Furthermore, the particularfeatures, structures or characteristics may be combined in any suitablecombinations and/or sub-combinations in one or more embodiments orexamples. Particular features, structures or characteristics may beincluded in an integrated circuit, an electronic circuit, acombinational logic circuit, or other suitable components that providethe described functionality. In addition, it is appreciated that thefigures provided herewith are for explanation purposes to personsordinarily skilled in the art and that the drawings are not necessarilydrawn to scale.

As used herein, a “wafer” is a thin slice of crystalline material, suchas silicon carbide, used in the fabrication of semiconductor devices andintegrated circuits. The term “substrate” refers to the semiconductorsupporting material upon which or within which the elements of asemiconductor device are fabricated, which substantially comprises thethickness of a wafer. Upon completion of the fabrication process thewafer is typically scribed and broken into individual semiconductor die,each of which consists of one or more semiconductor devices.

In the context of the present application, when a diode is in an “offstate” or “off” the diode does not substantially conduct current.Conversely, when a diode is in an “on state” or “on” the diode is ableto substantially conduct current in a forward-biased direction.

It is appreciated that each the diode structures shown and disclosedherein may represent a single device cell or unit. Each of the diodecells shown may be replicated in a mirrored or translated fashion manytimes in in two-dimensional layouts across a wafer to form a completelyfabricated SiC device.

A SiC counter-doped Schottky diode that incorporates a relatively thinor shallow P-type layer at the surface of the semiconductor layer tosubstantially reduce the surface electric field, and hence thereverse-bias leakage current, is described. The doping and thickness ofthe P-type layer are determined to insure that the P-type layer iscompletely depleted at zero bias. In the off-state, thenegatively-charged acceptors in the depleted P-type layer reduce theelectric field at the Schottky metal interface, thereby reducing thereverse leakage. It has been demonstrated that the counter-dopedSchottky diode disclosed herein has a lower electric field at thesurface as compared with a conventional Schottky diode. Compared to aconventional JBS diode, the counter-doped Schottky diode has a Schottkyinterface over the entire anode and hence conducts with lower resistancein forward bias.

FIG. 2 is an example cross-sectional diagram of a SBD 20 fabricated in aSiC wafer. As shown, SBD 20 includes a counter-doped Schottky barrierhaving spaced-apart, shallow P-type layers or regions 22 a & 22 bdisposed at a top planar semiconductor surface 23 beneath and in directcontract with top metal layer 21, which forms the anode of SBD 20. Metallayer 21 may comprise titanium or other suitable Schottky metal, e.g.,molybdenum nitride.

By way of example, in a typical 1200 V counter-doped Schottky barrierdiode, P-type regions 22 a & 22 b are shown disposed in an upper N+current spreading layer (CSL) or region 27 to predetermined implantdepth of about 100 nm, or less, beneath top planar surface 23. EachP-type region may have a doping concentration in a range of about1E16/cm³ to 2E16/cm³. Within this combined doping range and thickness,P-type regions 22 a & 22 b are fully depleted at zero bias, so as toavoid introducing an additional forward voltage drop in the on-state(forward biased).

In one embodiment, the lateral width of P-type regions 22 a & 22 b isabout 500 nm. P-type region 22 a is laterally separated from P-typeregion 22 b by a distance of about 0.5 μm. It should be appreciated thatSBD 20 with shallow P-type regions 22 effectively reduces the electricfield at surface 23 without impacting forward bias current. Unlike theconventional JBS diode structure shown in FIG. 1 , in SBD 20 the entireregion beneath top metal layer 21 is available for forward conduction.In other words, because P-type regions 22 a & 22 b are very shallow andfully depleted in forward bias, the entire region directly beneath topmetal layer 21 acts as a Schottky diode.

Practitioners in the art will further appreciate that compared withconventional JBS diodes SBD 20 has an advantage of being much narrowerin pitch while reducing reverse bias leakage current considerably, butwithout a significant reduction in forward current.

Continuing with the example of FIG. 2 , N+ CSL 27 extends verticallyfrom top planar surface 23 down to an N-type drift region 24. N-typedrift region 24 separates N+ CSL 27 from underlying N+ SiC substrate 28.A bottom metal layer 26, which is disposed directly beneath N+ SiCsubstrate 28, forms the cathode of SBD diode 20.

In one embodiment, for a 1200 volt diode N-type drift region 24 may havea doping concentration of about 9E15/cm³ and a thickness of about 10 μm.SiC substrate 28 may have a doping concentration of about 4E18/cm³ and athickness in a range of 100 μm to 360 μm.

It is appreciated that in other embodiments the depth or thickness ofP-type regions 22 a & 22 b may be less than or slightly greater than 100nm (e.g., 120 nm) while still insuring that P-type regions 22 a & 22 bare fully depleted at zero bias. Considering only depletion due to thePN junctions, the extent or width WI of the depletion region in each ofP-type regions 22 a & 22 b is given as

$W_{P} = \sqrt{\frac{2ɛ_{S}}{{qN}_{A}}\frac{kT}{q}\left( \frac{N_{D}}{N_{A} + N_{D}} \right){\ln\left( \frac{N_{A}N_{D}}{n_{i}^{2}} \right)}}$

where N_(A) and N) are the doping concentrations of the P-type andN-type regions 22 and 27, respectively, ε_(S) is the semiconductordielectric constant, q is the electronic charge, k is Boltzmann'sconstant, T is absolute temperature, and n_(i) is the intrinsic carrierconcentration at temperature T. For a given P-type doping N_(A), keepingthe thickness (depth) of each P-type region 22 less than W_(P) insuresthat each P-type region 22 is totally depleted at zero bias.

In counter-doped SBD 20, the holes in the P-type regions 22 are depletedby diffusing both to the N-type region 27 on one side, and to the topmetal layer 21 on the other side where they recombine with freeelectrons. When the anode is raised to a positive potential thedepletion region in each of the shallow, counter-doped P-type regions 22contracts from both ends. However, by careful selection of the top metaland the combined doping concentration and thickness, each counter-dopedP-type region 22 is kept depleted even at the rated forward biasoperating condition of the diode.

Conversely, when the anode is negative the depletion region of the PNjunction expands into each P-type region 22. Thus, if P-type regions 22are totally depleted at a zero bias condition, they remain depleted atall non-zero reverse biases.

Practitioners in the art will appreciate that to a first order,inclusion of shallow P-type regions 22 beneath top metal layer 21 has aminimal effect on the on-state (forward bias) performance of diode 20.In reverse bias the electric field at the metal-semiconductor interfaceis substantially reduced in counter-doped SBD 20, as compared withconventional SBD devices.

It should also be noted that in certain embodiments the P-type region 22doping-thickness product may be less than N_(A)×W_(P). For example, thedoping of P-type regions 22 can be reduced to zero (an intrinsic layer),or even become slightly N-type provided that remains more lightly dopedthan N-type drift region 24.

It is further appreciated that in still other embodiments N+ CSL 27 mayoptionally be eliminated such that the N-type drift region 24 extendsupward to top surface 23.

FIG. 3 an example cross-sectional diagram of a JBS diode 30 withcounter-doping in the Schottky region. The device structure of JBS diode30 includes a single shallow, implanted P-type region or layer 32 thatextends laterally across the top SiC surface 39. Top metal layer 31(anode) is disposed above, and in direct contact with, P-type layer 32,which, in one embodiment, is formed via ion implantation to a depth ofabout 100 nm, or less, beneath surface 39. Disposed beneath P-type layer32 are laterally spaced-apart, highly-doped deep P+ JBS regions 33 a &33 b.

In one embodiment, P+ JBS regions 33 are disposed in N+ CSL region 37with each having a lateral width of about 2.0 μm and a vertical depthtypically of about 0.3 μm to 1.5 μm. In certain embodiments, P+ JBSregions may be formed to a depth of 1.0 μm. P+ JBS regions 33 a & 33 bmay be doped to a concentration of 1E19/cm³ to 2E20/cm³. N+ CSL 27extends vertically from top surface 39 down to an N-type drift region34. N-type drift region 34 vertically separates N+ CSL 37 fromunderlying N+ SiC substrate 38. A bottom metal layer 36, which isdisposed directly beneath N+ SiC substrate 38, forms the cathode of JBSdiode 30.

As was the case with SBD 20 shown in FIG. 2 , P-type layer 32 of JBSdiode 30 has a doping concentration and depth that is selected such thatP-type layer 32 is completely depleted of carriers at zero bias. Becauseshallow P-type layer 32 extends across top surface 39 beneath the entirelateral width of metal layer 31 the electric field at top surface 39 issubstantially reduced under reverse bias, as compared with conventionalJBS devices, thereby decreasing leakage current.

Practitioners skilled in the art will appreciate that the inclusion ofP-type layer 32 beneath top metal layer 31 advantageously improveson-state (forward bias) performance of JBS diode 30, as compared withconventional JBS devices. In addition, the incorporation of shallowP-type layer 32 in combination with heavily-doped, deep P+ JBS regions33 functions to further reduce reverse bias leakage current as comparedto the prior art JBS diodes.

FIG. 6 is chart showing reverse-bias leakage current performance resultsfor two embodiments of the JBS diode illustrated in FIG. 3 versus theconventional JBS diode of FIG. 1 . The reverse-bias performance resultsfor the conventional JBS diode with no shallow counter-doped P-typelayer is shown at the top of the chart. The reverse-bias performanceresults for two embodiments of a 1200 V rated JBS diode having shallow,P-type counter-doping—with respective doping/thickness combinations of1E16/cm³/100 nm and 2E16/cm³/100 nm—are shown on the bottom two lines ofthe chart. As can be seen, the counter-doped JBS diodes providesignificantly reduced reverse bias leakage current at all voltages.

FIG. 4 is an example cross-sectional diagram of a trench JBS diode 40fabricated by deeply etching areas of N+ CSL 47 to form a semiconductor(SiC) mesa defined by respective trenches 62 a and 62 b. The mesacomprises a top portion of N+ CSL 47 that includes vertical sidewalls 61a & 62 b respectively disposed on opposite sides of the mesa. Sidewalls61 and the top surface 49 of the SiC mesa are counter-doped via ionimplantation to form a shallow P-type region or layer 42 that extendsvertically along sidewalls 61 and horizontally beneath top surface 49.It is appreciated that sidewall counter-doping may be performed byangled ion implants that form P-type layer 42 along sidewalls 61 a & 61b, during which time top surface 49 is masked.

After removal of the masking layer a vertical implant may be performedto form the horizontal portion of P-type layer 42 beneath top planarsurface 49. Following formation of the counter-doped horizontal andvertical portions of P-type layer 42, top metal layer 41 may be formeddirectly on P-type layer 42 on both the top and sidewall portions of themesa, as well at the bottom of trenches 62 in contact with P+ regions43. Top metal layer 41 forms a Schottky contact which functions as theanode of trench JBS diode 40.

Like the previous embodiments discussed above, shallow P-type layer 42may be formed to a depth or thickness of about 100 nm or less along thetop and sidewall areas of the SiC mesa. For a given top metal type(e.g., titanium), the depth and doping concentration of P-type layer 42,along with the doping concentration of N+ CSL 47 are selected to insurethat P-type layer 42 is fully depleted at zero applied bias.

Also shown in FIG. 4 , are heavily-doped P+ JBS regions 43 a & 43 brespectively disposed directly beneath the bottom of trenches 62 a & 62b. In one embodiment, the doping of P+ JBS regions 43 is in a range ofabout 1E19/cm³ to 2E20/cm³. The depth of each P+ region 43 may typicallybe about 0.2-0.4 μm for trenches 62 etched to a depth in a range fromabout 0.5-1.0 μm.

Note that in the example of FIG. 4 the depth of each P+ JBS region 43does not extend to the bottom of N+ CSL 47, which is directly aboveN-type drift region 44. N-type drift region 44 vertically separates N+CSL 47 from underlying N+ SiC substrate 48. A bottom metal layer 46,which is disposed directly beneath N+ SiC substrate 48, forms thecathode of trench JBS diode 40.

Persons of skill in the art will understand that N+ CSL 47 mayoptionally be omitted in certain embodiments such that N-type driftregion 44 extends vertically from substrate 48 to the counter-dopedP-type layer 42 at the top of the mesa. In one embodiment, N+ CSL 47,when included, has a doping concentration is a range from about 2E16/cm³to 1E17/cm³. In the example of FIG. 4 the SiC mesa may have a height(equal to the depth of trenches 62) in a range of about 0.5-1.0 μm, anda lateral width of about 1.0-2.0 μm.

It is appreciated that in trench JBS diode 40 shown in FIG. 4 ,shielding of the electric field in reverse bias from the implanted P+JBS regions 43 at the bottom of the trench is enhanced by the shallowcounter-doping implant utilized to form P-type layer 42 along thevertical sidewall portions and horizontal top portion of the SiC mesa.Electric field shielding is provided from the trench bottom P+ JBSregions 43, and from the shallow P-type layer 42 disposed alongsidewalls 61, as well as from shallow P-type layer 42 disposed at topplanar surface 49 of the SiC mesa, which surface forms a Schottkybarrier contact.

FIG. 5 is an example cross-sectional diagram of another trench JBS diode50 where the sidewalls 71 a & 71 b of trenches 72 a & 72 b arecounter-doped by implant to form shallow vertical sidewall P-typeregions or layers 52 a & 52 b, respectively. Top planar surface 59 ofthe SiC mesa comprising N+ CSL 57 is not counter-doped. Top metal layer51 directly contacts the mesa-top as well as the top of P-type regions52 a & 52 b at top surface 59 of the SiC mesa. Top metal layer 51 alsocontacts the P-type regions 52 on the trench sidewalls as well as the P+JBS implant regions at the bottom of trenches 72.

The example trench JBS diode 50 of FIG. 5 is identical to trench JBSdiode 40 shown in FIG. 4 in all respects except that the shallow P-typecounter-doped layer is omitted at the horizontal mesa-top area of N+ CSL57. That is, top surface 59 of N+ CSL 57 directly contacts top metallayer 51. P+ JBS regions 53 a & 53 b are formed beneath trenches 72 a &72 b. Each P+ JBS region 53 shields both the sidewall Schottky barrierand the mesa-top Schottky barrier. Practitioners will appreciate thatP-type counter-doped regions 52 along the mesa sidewalls adds to theshielding of the Schottky barrier at the mesa-top by the JBS regions 53.

Persons of ordinary skill will understand that the sidewall Schottkybarrier is exposed to higher electric fields than the mesa-top, but italso has a higher effective Schottky barrier due to the counter-dopedP-type regions 52 disposed along the vertical sidewall areas; hence,P-type regions 52 further shield the mesa-top Schottky barrier.

The depth and doping concentration of P-type regions 52, disposed alongthe sidewalls of the mesa are selected, along with the dopingconcentration of N+ CSL 57, to insure that, for a given top metal type,P-type regions 52 are fully depleted at zero bias. As shown, N-typedrift region 54 is formed over N+ SiC substrate 58. A bottom metal layer56, which is disposed directly beneath N+ SiC substrate 58, forms thecathode of trench JBS diode 50.

Persons of skill in the art will understand that N+ CSL 57 is optionaland may be omitted in certain embodiments, such that N-type drift region54 extends vertically from substrate 58 to top surface 59 of the mesa.In one embodiment, N+ CSL 57 has a doping concentration is a range fromabout 2E16/cm³ to 1E17/cm³. In the example of FIG. 5 the SiC mesa has aheight (depth of trenches 72) in a range of about 0.5-1.0 μm, and alateral width of about 1.0-2.0 μm.

The above description of illustrated example embodiments, including whatis described in the Abstract, are not intended to be exhaustive or to belimited to the precise forms or structures disclosed. While specificembodiments and examples of the subject matter described herein are forillustrative purposes, various equivalent modifications are possiblewithout departing from the broader spirit and scope of the presentinvention. Indeed, it is appreciated that the specific examplethicknesses, material types, concentrations, voltages, etc., areprovided for explanation purposes and that other values may also beemployed in other embodiments and examples in accordance with theteachings of the present invention.

We claim:
 1. A Junction Barrier Schottky (JBS) diode comprising: asilicon carbide (SiC) substrate of a first conductivity type; an upperregion having a first doping concentration of a first conductivity type,the upper region being disposed above the SiC substrate, the upperregion having a top portion defined as a mesa by first and secondtrenches, the mesa having first and second sidewalls and a top planarsurface: a shallow layer of a second conductivity type disposed in themesa extending horizontally along the top planar surface and extendingvertically along the first and second sidewalls down to a bottom of thefirst and second trenches, respectively, the shallow layer having athickness and a second doping concentration, the thickness being lessthan a width of a depletion region in the shallow layer such that theshallow layer is completely depleted at a zero bias condition of the JBSdiode; a top metal layer disposed along the top planar surface, thefirst and second sidewalls, and the bottom of each of the first andsecond trenches, the top metal layer being in direct contact with theshallow layer along the top planar surface and the first and secondsidewalls, the top metal layer comprising an anode of the Schottkydiode; first and second deep regions of the second conductivity type,the first and second deep regions being disposed in the upper regiondirectly beneath and adjoining the bottom of the first and secondtrenches, respectively, the first and second deep regions extendingdownward to a vertical depth substantially greater than the thickness ofthe shallow layer, the first and second deep regions being laterallyspaced-apart, each of the first and second deep regions having a thirddoping concentration substantially greater than the second dopingconcentration, the top metal layer being in direct contact with thefirst and second deep regions; and a bottom metal layer disposed beneaththe SiC substrate, the bottom metal layer comprising a cathode of theJBS diode, wherein the upper region comprises an N+ current spreadinglayer (CSL), and further comprising an N-type drift region disposeddirectly beneath the N+ CSL, the N-type drift region verticallyseparating the N+ CSL from the SiC substrate.
 2. The JBS diode of claim1 wherein the thickness of the shallow layer is about 100 nm or less. 3.The JBS diode of claim 1 wherein the first conductivity type is N-typeand the second conductivity type is P-type.
 4. The JBS diode of claim 3wherein the vertical depth is in a range of about 0.2 μm to 0.4 μm. 5.The JBS diode of claim 4 wherein the second doping concentration is in arange of about 1E16/cm³ to 2E16/cm³, and the third doping concentrationis in a range of about 1E19/cm³ to 2E20/cm³.
 6. The JBS diode of claim 1wherein the first and second deep regions are laterally spaced-apart bya distance substantially equal to a lateral width of the mesa.